α,β-Unsaturated ketones or aldehydes are important fine chemicals widely used not only in general organic synthesis, such as in Michael additions and Diels-Alder reactions, etc., but also in the cosmetic and personal care industries. For example, Hedione®(methyldihydrojasmonate) is an important fragrance component used in many commercial blends. Preparation of α,β-unsaturated ketones or aldehydes from more readily available simple ketones and aldehydes, respectively, through oxidation of the corresponding enolates is known, for example, through the Saegusa oxidation of enol silyl ether (Ito, Y.; et al., J. Org. Chem. 1978, 43, 1011-1013); however, this synthetically important transformation often requires relatively high palladium loadings (e.g., oxidation of trimethylsilyl ether of cyclohexanone to form 2-cyclohexen-1-one requires 0.5 equivalents of Pd(OAc)2), which severely limits its utility in commercial scale syntheses of compounds that would be used for personal care or pharmaceutical industries.
Similarly, α-halo ketones or aldehydes are versatile synthetic building blocks not only because they can serve as precursors to α,β-unsaturated ketones and aldehydes, but they can be converted into many other compounds through nucleophilic substitution of the α-halogen, in particular an α-bromo group. Therefore, synthesis of α-halo, in particular α-bromo, ketones or aldehydes is of great synthetic value.
Although copper(II) halides have been known to effect α-bromination or chlorination of ketones for over half a century (see, e.g., Kosower, E. M.; et al., J. Org. Chem. 1963, 28, 633-638; Kosower, E. M.; et al., J. Org. Chem. 1963, 28, 630-633; Kochi, J. K., J. Am. Chem. Soc. 1955, 77, 5274-5278), oxidation of enol acetates by copper salts have not been reported or used to effect such desired chemical transformations at commercial scales. Because copper(II) salts are inexpensive and abundant and less toxic than precious metals such as palladium, their use in the synthesis of organic compounds, especially those used for personal care and pharmaceutical products, remains underexplored.